Sand shield jet sled

Abstract

An apparatus for burying a pipeline in a seabed comprising unconsolidated materials such as sand. The apparatus includes a jet sled having jetting legs for disposition on opposite sides of the pipeline to direct a stream of high pressure water into the seabed to form a trench for the pipeline, and an elongate member extending rearwardly of the jet sled having shields depending therefrom to physically restrain the walls of the trench from caving-in and filling the trench beneath the unsupported portion of the pipeline. In addition, fluid jet nozzels are carried along each of the shields providing a mild turbulence at the lower edge of the shields to assist in keeping sand out of the trench and maintain the bottom of the trench in a fluidized condition. The elongate member comprises a pair of ballast tanks which may be selectively ballasted or deballasted to raise and lower the sand jet sled apparatus within the water, and to assist the settling of the pipeline into the seabed.

What is claimed is: 
     
       1. Apparatus for entrenching a submerged pipeline in a seabed, comprising: a jet sled adapted to straddle the submerged pipe laying on the seabed, said jet sled having jet legs depending downwardly therefrom for forming a trench in the seabed for the pipeline;   an elongate member extending from the rear of the jet sled; and   shields attached to said member and disposed on opposite sides of the unsupported portion of the pipeline extending from the surface of the seabed to the bottom of the trench, said shields preventing unconsolidated material from filling in the trench beneath the unsupported length of the pipeline.   
     
     
       2. The apparatus of claim 1 further comprising jetting means carried by said shields for directing a flow of pressurized fluid outwardly from said shields to assist in preventing unconsolidated material from filling the trench. 
     
     
       3. The apparatus of claim 1 wherein said jet sled comprises first and second outriggers extending laterally of said elongate member on opposite sides of the submerged pipeline to support the jet sled over the submerged pipeline. 
     
     
       4. The apparatus of claim 3 wherein said outriggers are pivotally attached to said elongate member and are adjustable to dispose said jet legs at various depths within the seabed. 
     
     
       5. The apparatus of claim 4 wherein said outriggers comprise: a mounting frame having a hinge formed thereon; and   a pontoon secured to said mounting frame for sliding along on the seabed surface.   
     
     
       6. The apparatus of claim 1 wherein said elongate member comprises at least one elongate ballast tank disposed substantially symetrically about the centerline axis of the elongate member. 
     
     
       7. The apparatus of claim 6 wherein each of said ballast tanks is provided with at least one flooding valve for admitting liquid ballast material into said tank, and further provided with a source of pressurized gas for expelling the liquid ballast material from said tank. 
     
     
       8. The apparatus of claim 7 wherein each of said ballast tanks is divided into a plurality of separate ballastable and deballastable chambers. 
     
     
       9. The apparatus of claim 6 further comprising: means to selectively ballast and deballast said ballast tank to sink said elongate member to the seabed and to raise said elongate member to the surface.   
     
     
       10. The apparatus of claim 1 wherein the jet legs on said jet sled comprise: forward fluid jet conduits having a plurality of nozzles formed thereon for directing a stream of high pressure fluid into the seabed ahead of said jet sled;   a set of vertically oriented rollers disposed inwardly toward the pipeline; and   an exhaust mechanism for drawing dislodged seabed material from the area of the trench inside said shields and depositing dislodged material to the side of the trench outside the shields.   
     
     
       11. The apparatus of claim 1 wherein said shields are plates that depend vertically, downwardly from said elongate member extending over a portion of the length of said elongate member and having a depth dimension that approximates the depth of the trench formed by said jet legs. 
     
     
       12. The apparatus of claim 1 wherein: said elongate member carries a series of rollers spaced at locations therealong for bearing engagement with the pipeline, each one of said rollers from the forward to the aft portion of the elongate member extending a greater distance into the trench than the preceding roller; and   said elongate member carries ballast to create a downward force acting on the pipeline through said series of rollers to force the pipeline into the trench.   
     
     
       13. Apparatus for entrenching a submerged pipeline in a seabed, comprising: an elongate member having jetting nozzles attached thereto and disposed on opposite sides of the pipeline to fluidize the seabed proximate the pipeline;   a series of rollers carried by said elongate member spaced at locations therealong for bearing engagement with the pipeline, each one of said rollers from the forward to the aft portion of the elongate member extending a greater distance beneath the elongate member than the preceding roller; and   a ballast carried by said elongate member to increase the submerged weight thereof and increase the downward force applied to the pipeline through said rollers to fore the pipeline into the seabed.   
     
     
       14. The apparatus of claim 13 wherein said elongate member comprises at least one ballast tank, with said ballast being contained within the tank. 
     
     
       15. The apparatus of claim 14 further comprising means to selectively ballast and deballast said ballast tank to adjust the downward force acting on the pipeline. 
     
     
       16. Apparatus for entrenching a submerged pipeline in a seabed consisting of unconsolidated material, comprising: first and second jet legs disposed on opposite sides of the submerged pipeline for forming a trench within the seabed to accommodate the pipeline;   an elongate ballast tank extending rearwardly of said first and second jet legs;   port and starboard outriggers, each mounted to said elongate ballast tank and adapted to straddle the submerged pipeline laying on the seabed;   first and second shields, each attached to said ballast tank, for disposition on opposite sides of the submerged pipeline inside the walls of the trench, said shields extending the length of the unsupported portion of the pipeline between the surface of the seabed and the bottom of the trench to prevent unconsolidated seabed material from filling the trench before the pipeline has sunk to the desired depth within the trench; and   means to selectively ballast and deballast said elongate ballast tank to raise and lower the trenching apparatus between a submerged seabed location and the surface of a body of water.   
     
     
       17. The apparatus of claim 16 further comprising jetting means associated with each of said shields for directing a flow of pressurized fluid outwardly from said shields against the walls of the trench to assist in preventing unconsolidated seabed material from entering the trench beneath the pipeline. 
     
     
       18. The apparatus of claim 17 wherein said ballast tanks is segmented into a plurality of separate chambers. 
     
     
       19. The apparatus of claim 18 wherein said outriggers are pivotally attached to the side of said ballast tank with adjustment means attaching to the outriggers to effect various depths of penetration of said jetting legs into the seabed. 
     
     
       20. The apparatus of claim 19 wherein said jet legs each comprise a plurality of fluid jet nozzles being supplied high pressure water from a manifold, and include an air lift mechanism for removing dislodged seabed material from within the trench formed. 
     
     
       21. The apparatus of claim 16 wherein: said elongate member carries a series of rollers spaced at locations therealong for bearing engagement with the pipeline, each one of said rollers from the forward to the aft portion of the elongate member extending a greater distance into the trench than the preceding roller; and   said elongate member carries ballast to increase the downward force applied to the pipeline through said series of rollers and force the pipeline into the trench.